1. Field of the Invention
The present invention relates to a battery system and particularly to a battery system including a plurality of cells with a series-parallel connection.
2. Description of the Related Art
Battery systems are known which include a plurality of battery elements connected in parallel, each of the battery elements including cells (battery cells) connected in series.
JP 2003-244854 A discloses the battery system providing a high storage capacity in a whole of a power storage system by connecting a plurality of storage devices in parallel, each of the storage devices including a plurality of module batteries connected in series, each of the module batteries including a plurality of battery cells directly connected in series. In addition, each storage device includes a voltage sensor for detecting a cell voltage of each cell, a voltage sensor for detecting a voltage across terminals in the whole of the storage device, and a current sensor for detecting a current flowing through the storage device, etc. to increase a reliability and safeness of the storage device.
As a scale of the storage devices become large, a total number of the cells included in the storage device becomes very large. Accordingly, when a cell voltage of each cell is detected, there are difficulties in processing data and cost because the number of the voltage detectors and an amount of the detection voltage data become very large. In such a circumstance, it is desired to provide a battery system in which the number of voltage detecting points for the cells is reduced as possible as reliability and safeness of the storage device are kept.
However, it is difficult to reduce the number of voltage detection points for the cells because the conventional art aimed such an operation that states of cells forming the storage device are homogenized.